<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<!--width height 会和padding+content+border冲突-->
<button style="margin: 20px;padding: 20px;">this is button</button>
<button style="width: 100px;height: 40px;">this is button</button>
</body>
</html>
